The present invention relates to a method and apparatus for improving the production of an oil well.
More specifically, the present invention relates to a method and apparatus for improving the production of an oil well, which is being artificially produced by the gas-lift technique.
As is well known, the gas-lift technique is employed in wells, typically oil wells, which have difficulty in producing naturally. That is, wells in which the formation pressure is not sufficient to cause the well to produce at an acceptable volume. The gas-lift technique injects gas into the casing, which has been sealed or packed off at the bottom of the hole relative to the production tubing. A gas-lift valve is placed in the production tubing at the production level, and the gas-lift valve permits the gas to be injected into or bubble into the fluid being produced from the well. The gas passes very slowly through the gas-lift valve and bubbles into the column of fluid, which is in the producing tubing. This gas then makes the fluid in the production tube somewhat lighter and, hence, the natural formation pressure will be sufficient to push the fluid up and out of the well. This means that the well can be produced at a greater rate. The gas-lift technique described above is known as continuous gas-lift.
An adaption of this gas-lift technique is known as intermittent gas-lift. In this technique, rather than letting the gas enter the production tube slowly, the gas is injected into the production tubing very quickly, thereby forming a large slug of fluid in the production tubing above the injected gas bubble. The gas bubble then drives the slug of fluid in the production tubing upwardly. The intermittent technique is repeated successivley, thereby producing successive slugs of fluid at the wellhead.
In order to optimize production employing either of these two gas-lift methods, it is necessary to unergo trial and error operation to determine the specific parametric values relative to the gas-lift injectin. For example, in the continuous gas-lift method it is necessary to undergo a trial and error period to determine the optimum injection rate of gas into the well necessary to maximize production. Similarly, in the intermittent gas-lift method, it is necessary to determine not only the optimum gas-lift pressure to be injected into the production tubing, but also the periodicity of the discreet gas injections. As expected, in the intermittent method, if the gas is injected too frequently, the slug of fluid formed above the gas bubble will not be large enough to maximize production of the well. Similarly, if the time between successive injections is too long, valuable production time is lost. Both of these two types of gas-lift production techniques are improved by the present invention.
The existence of increased temperatues in the earth's core has been well-known for some time. Specifically, it is known that as one progresses deeper and deeper into the earth's core the temperature increases accordingly. This is termed the geothermal gradient of the earth. While the fact that the temperature increases with depth is a general rule, the extent of the gradient varies at different locations around the earth and is generally not the same for any two wells. The effect of this geothermal gradient is that the liquid being produced from reservoirs at the same depth will appear at the respective wellheads at different temperatures.
Although this geothermal gradient has been well-known and the gas-lift technique has become more and more popular, the combination of this geothermal gradient phenomenon with the gas-lift technique has not heretofore provided advantageous results. Nevertheless, there has been a correlation shown between the temperature of the fluid produced at the wellhead in a gas-injected well and the optimum rate of liquid flow. Such correlation is briefly discussed in the textbook by K. E. Brown, Gas Lift Theory And Practice, Prentice-Hall, Inc. At page 115, Mr. Brown shows a graph indicating the surface flowing temperature of the fluid at the wellhead plotted against the gas/liquid ratio of the gas injected system. Various curves for different production rates at the well head are shown. Nevertheless, there is no discussion of how to arrive at the optimum gas/liquid ratio.